Electrolytic recording process and materials



Patented Oct. 24, 1967 3,349,013 ELECTROLYTIC RECORDING PROCESS AND MATERIALS Eugene F. Barnes, Arlington Heights, and Carole N.

Urbanski, Elmwood Park, Ill., assignors to Stewart- Warner Corporation, Chicago, Ill., a corporation of Virginia No Drawing. Filed Jan. 22, 1964, Ser. No. 339,346 19 Claims. (Cl. 2042) This invention relates to an electrolytic recording process and materials employed therein. More particularly, the invention relates to a process and materials for electrolytic facsimile recording on an electrolytically conducting recording medium.

Electrolytic facsimile recording as currently practiced utilizes the electrolytic action of an electric current on an anode and an electrolytically conducting recording medium in contact therewith and with a cathode for direct facsimile recording. Graphic copy is scanned at a remote point, and a direct current potential corresponding in intensity to the density of the copy being scanned is applied to the electrodes. The recording current is localized to produce marks on the recording medium corresponding to the copy being scanned. It is common practice to dispose a recording medium having a paper base between intersecting electrodes with at least one of the electrodes in motion to accomplish progressive movement of their intersection along a line to thereby record along such line. The recording medium is drawn past the electrodes at a regular rate to accomplish line by line recording. Suitable facsimile communications apparatus is disclosed, for example, in U.S. Patent No. 2,835,733. Illustrative types of recording apparatus are disclosed in U.S. Patents Nos. 2,063,992 and ,855. These patents illustrate recorders of the drum and helix type, which type is in widespread use.

A preferred process of electrolytic facsimile recording involves dissolution of an anodic metal in the recording medium upon passage of an electric current between the electrodes and through the medium. The anodic metal is electrochemically oxidized, so that it is transformed from the metallic state into soluble metal ions which dissolve in the medium. The recording medium is provided with a reagent that causes the dissolved metal to be deposited on the medium as a marking substance. The quantity of anodic metal dissolved and then deposited in this manner is a function of the intensity of the electric current, which in turn is a function of the density of color of the original graphic copy being scanned. In this manner, the densities of the recorded markings are made to vary in like manner to the copy being scanned, and the facsimile image is produced on the recording medium.

The above identified U.S. Patent No. 92. discloses recording compositions which are applied to absorbent sheet material such as paper to provide electrolytic recording media for use preferably with a silver anode. One composition is an alkaline electrolytically conducting solution containing formaldehyde reducing agent. In use, anodic silver dissolves in the medium by electrochemical oxidation of the free metal to soluble silver ions, and the dissolved silver is reduced to the free metal and deposits on the medium as a marking substance. Such a process is potentially attractive, inasmuch as good sensitivity is observed, direct reduction to free metal takes place with the formation of a permanent metal image, and only simple solutions and reactions are involved. However, as disclosed in the patent, reduction is relatively slow and the image exhibits extensive bleeding. Also, formaldehyde is fugitive, and it is objectionable in use.

The foregoing patent also discloses a refinement wherein the silver ions are first precipitated as silver halide, after which the halide is reduced to free metal with catechol (pyrocatechin). While this process constitutes an improvement, evaluation on present day equipment and at the printing speeds currently employed has shown that image formation still is slower than desirable. Catechol is undesirable in that is discolors articles in contact therewith, reacts readily with metal parts of machines and discolors them, and requires recording paper of hi h purity, lacking metal in the paper. Catechol requires a strong antioxidant when employed in a recording medium that is to be stored prior to use. The prints containing catechol darken with time, stain adjacent surfaces and transfer the image to other papers during storage. Both of the processes disclosed in the patent produce a brown colored mark rather than the preferred black mark, and the image density is too light at high speed.

transmission.

More recently, electrolytic recording media have been employed which produce a mark by formation of a color lake or complex with catechol or other phenolic compound in the media and a dissolved anodic metal, particularly, iron. These and other recording media suffer from various disadvantages. Those which employ catechol have the above disadvantages, and the recording media are relatively complex, requiring acids, precipitants or charge neutralizers, and oxidizing agents for increasing the range of color tones. At times, relatively high temperature heating is recommended for increasing the color density. In the absence of an oxidizing agent, the recording medium is limited in practice to relatively low recording speeds for achieving the desired color density. When an oxidizing agent is employed, the medium keeps working after recording, so that the prints darken with time. Consequently, different media are recommended for ditferent recording requirements. Recording media are also available which avoid the use of catechol. The marks produced with these media are lacking in density, the resolution of color tones is insufficient to meet certain requirements, and the preferred black colored marks are not produced.

It has now been discovered in accordance with the present invention that prior problems are overcome and marked advantages are obtainml by employing a formaldehyde sulfoxylate reducing agent in an electrolytically conducting recording medium for electrolytic facsimile recording by dissolution of an anodic metal in the medium and deposition of the dissolved metal on the medium as a marking substance. The invention provides a new electrolytic facsimile recording process embodying the use of a formaldehyde sulfoxylate reducing agent in the recording medium. A new composition of an electrolytically conducting solution containing the formaldehyde sulfoxylate is provided for incorporation in the recording medium. A new recording medium including a support or substrate impregnated with the new composition is provided for use in the new process.

The formaldehyde sulfoxylate in the recording medium reduces metal ions dissolved from the anode to the free metahwhich deposits on the recording medium as a marking substance. At the same time, the deposit may contain a precipitate formed by reaction of the metal ions with an oxidation product of the sulfoxylate. For example, when silveris employed as an anodic metal, silver sulfide may be present in the deposit. The action of the sulfoxylate is very rapid and complete, so that an excellent mark is produced even at high recording speeds and no noticeable change in the mark takes place after recording. No after treatment of the print is needed.

The invention provides exceptional recording currents and instantaneous marking over a wide range of printing speeds. The invention is universally applicable to present day recording requirements, so that but one recording medium need beemployed for all industrial and press publication uses. Excellent sharp, high density prints are produced, and the preferred blue-black color is readily provided. There is no discoloration of the recording medium before, during or after recording, no staining of other materials and objects, and no image transfer from the printed medium. It is not necessary to employ paper having a high degree of purity as the support in the recording medium. The new composition contains a minimum of ingredients, functions reliably in a relatively simple manner, is compatible with support materials, is easy to work with, and isnot injurious or objectionable to personnel.

Large volume commercial use imposes a requirement for aqueous electrolytic recording compositions and media which have good keeping qualities or stability, retaining their recording characteristics over storage periods extending for at least one month and preferably several months or more. The preferred embodiments of the invention also satisfy this requirement. In particular, the new composition preferably contains a combination of a formaldehyde sulfoxylate reducingagent and an alkaline salt which stabilizes or preserves the reducing agent. The composition preferably also has a pH in the range of about 10.5-12.5. The stability is outstanding at this pH, especially when the composition is employed with Wet strength paper as the support in the recording medium. The composition having such pH also provides a very favorable degree of alkalinity for acceleration of metal deposition to form a mark.

The preferred alkaline salt stabilizing agents include stannates, silicates, and aluminates. It is presently further preferred to employ a stannate as thesta-bilizing agent in the composition, for long continued storage stability. An especially advantageous composition also includes an alkaline buffer. The buffer serves to provide additional alkalinity for acceleration of metal deposition while maintaining a pH within the above range. The buffer provides even greater sensitivity and sharper printing, furnishing exceptional resolution and greater image density at constant current and voltage. An additional advantage is that anode or printer bar wear is reduced.

The formaldehyde sulfoxylate is a reducing compound containing the negative radical (CH OHSO The presently available formaldehyde sulfoxylates include the water soluble sodium formaldehyde sulfoxylate having the formula CH OHSO Na-ZH O and zinc formaldehyde sulfoxylates, including the water soluble zinc formaldehyde sulfoxylate having theformula (CH OHSO Zn.

sensitivity to certain uses, blue-black is the color of choice for universal application.

It is preferred to employ the formaldehyde sulfoxylate reducing agent in a concentration within a range of about 1-10% by weight of the recording composition. It is further preferred to employ a concentration in the range of about 3-6% by weight of the composition. At concentrations less than about 3%, the image density may decrease, and greater concentrations provide a safeguard against possible loss of reducing activity. At concentrations greater than about 6%, a longer aging period may be required for the recording medium to reach maximum activity. The concentration may vary somewhatwith the specific compound employed. For example, the zinc formaldehyde sulfoxylate appears to have greater reducing power under comparable conditions and therefore might be employed at a lower concentration than the sodium compound. The concentrations also are subject to change depending upon the conditions of use, including the recording or printing, conditions. The above and subsequently described concentrations refer to the respective compounds on an anhydrous basis.

The formaldehydesulfoxylate reducing agent may be employed in various aqueous alkaline compositions to produce good prints, particularly when using the preferred silver anode. The composition pH may range from about 8-125, above which range recording papers are likely to be deleteriously affected. For example, sodium formaldehyde sulfoxylate may be employed in a composition in which it is the only alkaline material. It may be employed together with a strong base, an alkaline buffer, or a combination thereof. Such compositions are suitable for use within a short period of time after being applied to a paper support, in the manner of the above Patent No. 2,063,992, for example. However, none of these compositions has been found suitable for application to the avail-,

strong bases and weak acids, particularly the sodium and potassium stannates, silicates, and aluminates. The stannates are especially preferable, because they provide long term storage stability, and they also provide optimum.

print color. It is preferred to employ the stabilizing agent in a proportion in the range of about 0.253%, more preferably 0.52% by weight of the composition. Greater concentrations may tend to change the color of the print, and lower concentrations may tend to reduce the density of the print and the storage stability, when otherwise practicing the invention in a preferred manner.

As previously described, the preferred pH of the composition containing the alkaline salt stabilizing agent is in the range of about 10.5-12.5. It is further preferred to provide a pH of about 11-12. Such pH preferably is provided by the alkalinity of the stabilizing agent. The pH is further regulated by the alkaline buffer when employed.

The alkaline buffers preferably are alkaline buffering salts which when dissolved in water provide a pH in the range of about 8-12. When employed together with the stabilizing agents, they maintain a pH in the range of about 10.5-42.5. They include, for example, soluble alkali metal and alkaline earth metal formates, acetates, carbonates, bicarbonates, borates, phosphates, tartrates and the like. Alkali metal formates, acetates and carbonates are especially preferred. The alkaline bulferpreferably is employed in a concentration in the range of about O.255%, more preferably 0.52% by weight of the composition. The concentration may vary, depending on the specific buffer employed and the remaining ingredients of the composition.

It is preferred to include a substantially neutral strong electrolyte in the composition, to provide suitable conductivity especially at higher recording currents. The electrolyte preferably is a soluble inorganic salt which does not interfere in the process of production or in the printing process. It is presently preferred to employ an alkali metal nitrate, especially potassium or sodium nitrate as the electrolyte. Other nitrates might be employed if desired, such as lithium, cesium, rubidium, or barium nitrate. The electrolyte preferably is employed in a concentration within the range of about 520%, more preferably 7l5% by weight of the composition. The image density increases at the lower concentrations and decreases at the higher concentrations.

In providing the new compositions, materials are selected which are compatible with each other, do not interfere with the process of manufacture or with the recording process, or affect the character of the prints. The materials preferably are colorless and impart no color to the prints. They are selected so as to minimize or obviate precipitation in the composition and precipitation on the medium which might affect the print. Thus, for example, cations which may precipitate hydroxides or oxides, such as calcium, and anions which may precipitate excessive amounts of silver or other anodic metal, such as chloride and sulfate, preferably are avoided. It is preferred not to employ ammonium salts, to preclude objectionable release of ammonia. Mixtures of stannates and borates will form precipitates and therefore are not recommended.

Preferably, water constitutes the balance of the composition. There is no requirement for special purpose materials, such as acids, precipitants, antioxidants, and other materials employed in prior printing compositions.

The composition is compounded by dissolving the ingredients in water up to a temperature of about 80 F. Preferably, the electrolyte is dissolved first, the formaldehyde sulfoxylate is dissolved next, and the remaining ingredients are dissolved last, followed by mixing. The resulting solution is allowed to stand overnight, during which time a slight gelatinous precipitate forms in the preferred compositions. The clear liquor is decanted and filtered, at which time it may be stored or employed for the preparation of the recording medium. The composition preferably is stored in a dark bottle or other container which protects the composition from light, at a preferred temperature of about 6575 F. Under such conditions, the preferred compositions have shelf lives of at least six months.

In providing the electrolytic recording medium, the composition preferably is applied to commercial wet strength paper as the support, to provide the type of medium which is most in demand. Either alkaline or acid wet strength paper may be employed, with the alkaline paper being preferred. The alkaline paper by nature is more compatible with the alkaline printing'composition, and optimum print color and density are obtained therewith. With some compositions, the acid paper may require more alkali in the composition and some precipitation may occur in the process of impregnating the paper. However, the resulting recording medium constitutes a good commercial product. If desired, the support may be cloth or other porous material compatible with the composition and with the recording process.

The recording composition may be applied to the support in any suitable conventional manner, such as by immersion or roller coating followed by removal of excess material. It is preferred to apply the composition to one side of a sheet, pass the sheet through squeeze rollers to distribute the composition therethrough and remove excess liquid, and wind the sheet in a roll. The quantity of composition remaining on the sheet preferably constitutes about 60% to 100% of the weight of the sheet on wet strength papers. The resulting recording medium preferably has a moisture content of about 30-40% by weight. The product may be packaged in opaque polyethylene bags or the like, which are heat sealed and placed in cartons or other containers. The resulting packages preferably are stored at a temperature of about 65- 75 F., under which conditions they have the stability described above. It is recommended for maximum print density that the product be aged about two Weeks when using the preferred compositions. Progressively longer aging periods are recommended for greater formaldehyde sulfoxylate concentrations where maximum density is desired.

The recording medium is well suited for use on commercial recording equipment such as described above, operating at any printing speed up to 900 drum revolutions per minute (r.p.m.) or lines per minute (l.p.m.). A linear knife edge anode and a helical wire cathode are currently employed in commercial equipment, similarly-to the apparatus illustrated in Patent No. 2,063,992. Silver is the preferred anodic metal, inasmuch as it produces a very desirable permanent print, is univalent with a valence of 1, has very favorable electrical and chemical characteristics, has desirable physical properties, and is rela tively economical. The pure metal or various alloys thereof may be employed. The alloys wear better and are less susceptible to distortion. It is presently preferred to employ an alloy containing at least about 45% of silver by weight. It is in general preferred to employ an alloy containing about 65% or more of silver at printing speeds up to 360 r.p.m., and to employ an alloy containing 7580% or more of silver at greater printing speeds. Any suitable alloying metals may be employed with silver. Alloys with copper and Zinc are readily available, and for this reason, such alloys are generally employed. If desired, other anodic metals which are reducible in the recording process may be employed, such as the noble metals gold, platinum, and palladium, and other metals such as iron, lead, and copper. The anode also may take other physical forms, e.g., a stylus may be employed. The cathode helix may be formed of any conducting material suitable for electrolytic recording. A noble metal alloy is preferably employed in the present commercial equipment, and stainless steel may be employed.

The recording medium preferably is used in the form of an impregnated roll of paper, as described above, and recording is accomplished in a recorder of the type described in Patent No. 2,202,855. Recording currents employing the preferred recording media preferably range from on the order of 20 milliamperes when recording at r.p.m. to about 200 milliamperes when recording at 900 r.p.m.

The printed sheet may be dried in any suitable manner. Drying is readily accomplished by passing the sheet over a heater bar mounted on the recorder, followed by exposure to the atmosphere. The heater bar may be maintained at about 100 F. when printing at 100 r.p.m., and the temperature may be raised for greater printing speeds, up to about 300 F. when printing at 900 r.p.m. The only function performed by the heater bar is to dry the sheet. The drying process may be accelerated by circulating air over the paper following exposure to the heater bar.

The resulting prints are permanent, and the color intensity remains constant. The prints are stable to normal atmospheric conditions, and they do not discolor on standing. The prints will not affect articles in contact therewith or transfer the image to other surfaces, so that they may be interfiled with other papers.

The following examples are illustrative of the invention. It will be understood that the invention is not limited to the examples or to the conditions, procedures, materials 7. and proportions employed therein. Unless otherwise stated, the proportions are by weight;

Example 1 The following compositions were compounded and impregnated in paper in a compressionzpaper weight ratio of 1: 1 in the manner described above:

Material Proportion, percent by weight Sodium formaldehyde sulloxylate 6. 6. O 6. 0 6. 0 Potassium nitrate 12.0 12.0 12.0 12. 0 Sodium stannate 1. 0 1. 0 .0 1. 0 Sodium iormatc... 1. Sodium acetate- Sodium carbonate 3 Water pH The composition was impregnated in commercial .alka-' line and acid wet strength papers. The paper stock was high purity alpha cellulose paper of 0.0026 inch average caliper, 1l /2-12 pound basis weight (500 sheets, 17 x 22 inches). The alkaline paper contained as the wet strength agent /2% by Weight based on the paper of a cationic water soluble polymer produced by crosslinking an essentially linear polyamide from saturated aliphatic dicarboxylic acid and polyalkylenepolyamine with epichlorohydrin and having a molecular Weight in the range of about 2000-5000 (Kymene 557). The acid paper contained as the wet strength agent 1% by weight based on the paper of melamine-formaldehyde resin. The

impregnated papers were formed into rolls 9 /2 inches wide, and the rolls were sealed in opaque polyethylene bags and stored at 6575 F. The impregnated papers.

Up to 360 r.p.m 65% silver, 25%

10% zinc.

From 360 to 900 r.p.m. 75% silver, 22% copper, 3% zinc, or 80% silver, 16% copper, 4% zinc.

copper,

The helical wire was a high temper, high fusion alloy of a major proportion of gold and containing silver as the principal alloying element. The recording currents were approximately as follows: 50 milliamperes at 100 r.p.m, 180 milliamperes at 360 r.p.m., and 200 milliamperes at 900 r.p.m.

Excellent blue-black prints were obtained with each paper at the several printing speeds. It was observed that the compositions containing formate, acetate or carbonate buffer provided greater density and outstanding resolution, being capable of resolving shades of black.

Example 2 The following composition was employed on alkaline wet strength paper in a composition:paper weight ratio of 0.9:1 with good results in the manner of Example 1.

Proportion, Material: percent by weight Sodium formaldehyde sulfoxylate 6.0 Potassium nitrate 10.0 Sodium stannate 1.0 Sodium formate 1.0 Water 82.0

The recording medium was used in press service work at rpm, employing the 75% silver printer bar of Example 1. The current intensity for maximum black was about 30 milliamperes, as compared to 100 milliamperes for the recording process previously employed.

Example 3 The following compositions were employed on alkaline wet strength paper with good results in the manner of Example 1 Material Proportion, percent by we ight Sodium formaldehyde sulfoxylate Potassium nitrate So lium orthosilicate 4 4 NaiSiO 5 N32310:

The impregnated papers have shelf lives of several,

months, as indicated, which is adequate for many pur poses.

Example 4 The following composition was employed on alkaline wet strength paper in the manner of Example 1.

Proportion,

Material: percent by weight Basic zinc formaldehyde sulfoxylate, about 0.07 Potassium nitrate 10.0 Sodium orthosilicate 1.0

Water Balance Example 5 The following compositions containing no stabilizing agent were found to be suitable for impregnation in paper and use in the manner of Example 1 within a short period of time after impregnation:

Material Proportion,

percent by weight Sodium formaldehyde sulioxylatc 3. 2 2. 5 Sodium nitrate... 15. 0 Potassium nitrate 12. 0 Sodium hydroxide 0.8 0.5 Sodium acetate... 3.0 Water 81. 0 82. 0 pH 12.5 11.3

Both compositions produced sharp prints having good density at recording speeds of and 360 r.p.m. The composition containing sodium acetate produced a blueblack print, and the remaining composition produced a brownish-black print. It is recommended that the recording media be used within about two days following impregnation when employing alkaline wet strength paper and immediately following impregnation when employing acid wet strength paper.

The invention thus provides an electrolytic recording process and materials employed therein which may be employed with all of the available recording machines over the entire range of printing speeds in current use, with results which correspond to the capacities of the sending and receiving units. The use of a formaldehyde sulfoxylate reducing agent overcomes the disadvantages U of prior materials and results in the production of excellent permanent prints. The recording compositions and media may be compounded to provide the stability necessary for various uses, and the preferred compositions provide shelf lives for the media which extend well beyond commercial requirements. The compositions and media are simple, effective and reliable, and they are readily manufactured and used on conventional equipment with no necessity for special procedures or precautions or for further treatment of the prints. The prints may be handled and stored conveniently, and the prints exhibit no changes in character or color during the use or storage.

It will be apparent that various changes and modifications may be made in the process and materials of the invention within its spirit and scope. It is intended that such changes and modifications be included within the scope of the appended claims.

We claim:

1. In a process of electrolytic facsimile recording wherein an anodic metal is dissolved in an electrolytically conducting recording medium by electrochemical oxidation of the metal to form soluble metal ions and the dissolved metal is deposited on the recording medium as a marking substance, the improvement which comprises employing as the recording medium a support impregnated with an electrolytically conducting solution containing a formaldehyde sulfoxylate reducing agent in an amount sufiicient to deposit said dissolved metal on the medium as a marking substance.

2. A process as defined in claim 1 wherein said anodic metal is silver.

3. In a process of electrolytic facsimile recording wherein an anodic metal is dissolved in an tlectrolytically conducting recording medium by electrochemical oxidation of the metal to form soluble metal ions and the dissolved metal is deposited on the recording medium as a marking substance, the improvement which com prises employing as the recording medium a support impregnated with an electrolytically conducting solution containing about 1-10% by weight of a formaldehyde sulfoxylate reducing agent to thereby deposit said dissolved metal on the medium as a marking substance.

4. In a process of electrolytic facsimile recording wherein an anodic metal is dissolved in an electrolytically conducting recording medium by electrochemical oxidation of the metal to form soluble metal ions and the dissolved metal is deposited on the recording medium as a marking substance, the improvement which comprises employing as the recording medium a support impregnated with an electrolytically conducting solution containing about 1-10% by weight of a formaldehyde sulfoxylate reducing agent and about 0.25-3% by weight of an alkali metal stannate, said solution having a pH of about 8-125, to thereby deposit said dissolved metal on the medium as a marking substance.

5. A process as defined in claim 4 wherein said formaldehyde sulfoxylate is selected from the group consisting of the alkali metal and zinc formaldehyde sulfoxylates, and said solution has a pH of about 10.5-12.5.

6. In a process of electrolytic facsimile recording wherein anodic silver metal is dissolved in an electrolytically conducting recording medium by electrochemical oxidation of the silver to form soluble silver ions and the dissolved silver is deposited on the recording medium as a marking substance, the improvement which comprises employing as the recording medium a paper support impregnated with an electrolytically conducting solution containing about 1-10% by weight of a formaldehyde sulfoxylate reducing agent, about 0.25-3% by Weight of an alkali metal stannate, an alkaline buffer, and analkali metal nitrate, said solution having a pH of about 10.5-12.5, to thereby deposit dissolved silver on the medium as a marking substance.

7. A process as defined in claim 6 wherein said formaldehyde sulfoxylate reducing agent is a compound selected from the group consisting of the alkali metal and zinc formaldehyde sulfoxylates.

8. In a process of electrolytic facsimile recording wherein anodic silver metal is dissolved in an electrolytically conducting recording medium by electrochemical oxidation of the silver to form soluble silver ions and the dissolved silver is deposited on the recording medium as a marking substance, the improvement which comprises employing as the recording medium a paper support impregnated with an electrolytically conducting solution containing about 3-6% by weight of sodium formaldehyde sulfoxylate, about 0.5-2% by weight of an alkali metal stannate, about 0.5-2% by weight of a compound selected from the group consisting of the alkali metal formates, acetates, and carbonates, and about 7-15 by weight of an alkali metal nitrate, said solution having a pH of about 10.5-12.5, to thereby deposit dissolved silver on the medium as a marking substance.

9. A composition for incorporation in an electrolytic recording medium for use in an electrolytic facsimile recording process wherein an anodic metal is dissolved in the recording medium by electrochemical oxidation of the metal to form soluble metal ions and the dissolved metal is deposited on the recording medium as a marking substance, which comprises an electrolytically conducting solution containing about 1-10% by weight of a formaldehyde sulfoxylate reducing agent and about 5-20% by weight of an alkali metal nitrate, said solution having a pH of about 8-125.

10. A composition for incorporation in an electrolytic recording medium for use in an electrolytic facsimile recording process wherein an anodic metal is dissolved in the recording medium by electrochemical oxidation of the metal to firm soluble metal ions and the dissolved metal is deposited on the recording medium as a marking substance, which comprises an electrolytically conducting solution containing about 1-10% by weight of a formaldehyde sulfoxylate reducing agent and about 0.25-3% by weight of an alkaline salt which stabilizes said reducing agent selected from the group consisting of stannates, silicates, and aluminates.

11. A composition for incorporation in an electrolytic recording medium for use in an electrolytic facsimile recording process wherein an anodic metal is dissolved in the recording medium by electrochemical oxidation of the metal to form soluble metal ions and the dissolved metal is deposited on the recording medium as a marking substance, which comprises an electrolytically conducting solution containing about 1-10% by weight of a formaldehyde sulfoxylate reducing agent and about 0.253% by weight of an alkali metal stannate, said solution having a pH of about 8-125.

12. A composition for incorporation in an electrolytic recording medium for use in an electrolytic facsimile recording process wherein an anodic metal is dissolved in the recording medium by electrochemical oxidation of the metal to form soluble metal ions and the dissolved metal is deposited on the recording medium as a marking substance, which comprises an electrolytically conducting solution containing about 110% by weight of a compound selected from the group consisting of the alkali metal and zinc formaldehyde sulfoxylates, and about 0.25-3% by weight of an alkali metal stannate, said solution having a pH of about 10.5-12.5.

13. A composition for incorporation in an electrolytic recording medium for use in an electrolytic facsimile recording process wherein an anodic metal is dissolved in the recording medium by electrochemical oxidation of the metal to form soluble metal ions and the dissolved metal is deposited on the recording medium as a marking substance, which comprises an electrolytically conducting solution containing about 3-6% by weight of an 11 alkali metal formaldehyde sulfoxylate, about 0.5-2% by weight of an alkali metal stannate, about 0.5-2% by weight of a compound selected from the group consisting of the alkali metal formates, acetates, and carbonates, and about 7-15% by weight of an alkali metal nitrate, said solution having a pH of about 10.5l2.5.

14. An electrolytic recording medium for use in an.

electrolytic facsimile recording process wherein an anodic metal is dissolved in the recording medium by electrochemical oxidation of the metal to form soluble metal ions and the dissolved metal is deposited on the recording medium as a marking substance, which comprises a support impregnated with'an electrolytically conducting solution containing about 110% by weight of a formaldehyde sulfoxylate reducing agent and about -20% by weight of an alkali metal nitrate, said solution having a pH of about 8-125.

15. An electrolytic recording medium for use in an electrolytic facsimile recording process wherein an anodic metal is dissolved in the recording medium by electrochemicaloxidation of the metal to form soluble metal ions and the dissolved metal is deposited on the recording medium as a marking substance, which comprises paper impregnated with an electrolytically conducting so lution containing about 1-10% by weight of a formaldehyde sulfoxylate reducing agent, about 0.255% by weight of an alkaline buffer, and about 520% by Weight of an alkali metal nitrate, said solution having a pH of about 10.5-12.5.

16. An electrolytic recording medium for use in an electrolytic facsimile recording process wherein an anodic metal is dissolved in the recording medium by electrochemical oxidationof the metal to form soluble metal ions and the dissolved metal is deposited on the recording medium as a marking substance, which comprises a.

support impregnated with an electrolytically conducting solution containing about 1-10% by weight of a formaldehyde sulfoxylate reducing agent and about 0.25-3% by weight of a member selected from the group consisting of alkali metal stannates, silicates, and aluminates.

17. An electrolytic recording medium for use in an electrolytic facsimile recording process wherein an anodic metal is dissolved in the recording medium by electrochemical oxidation of the metal to form soluble metal 12 dehyde sulfoxylate reducing agent and about 0.253% by weight of an alkali metal stannate,'said solution having a pH of about 10.5-12.5.

18. An electrolytic recording medium for use in an electrolytic facsimile recording process wherein an anodic metal is dissolved in the recording medium by electrochemical oxidation of the metal to form soluble metal ions and the dissolved metal is deposited on the recording medium as a marking substance, which comprises paper impregnated with an electrolytically conducting solution containing about 1-10% by weight of a compound selected from the group consisting of the alkali metal and zinc formaldehyde sulfoxylates, about (MS-3% by weight of an alkaline salt which stabilizes said reducing agent selected from the group consisting of stannates, silicates and aluminates, about 0.255% by Weight'of an alkaline buffer, and about 520% by weight of an alkali metal nitrate, said solution having a pH of about 19. An electrolytic recording medium for use in an electrolytic facsimile recording process wherein an anodic metal is dissolved in the recording medium by electrochemical oxidation of the metal to form soluble metal ions and the dissolved metal is deposited on the record- 1 ing medium as a marking substance, which consists essentially of paper impregnated with an electrolytically conducting solution containing about 36% by weight of sodium formaldehyde sulfoxylate, about 0.52% by weight of sodium stannate, about 0.52% by weight of sodium formate, about 7-15% by weight of potassium nitrate, and Water, said solutionhaving a pH of about 10.512.5.

References Cited UNITED STATES PATENTS 2,991,257 7/1961 Smith-Johannsen 252-606 3,113,910 12/1963 Hepher 2042 FOREIGN PATENTS 121,658 11/1943 Australia. 669,048 8/ 1963 Canada.

OTHER REFERENCES The Condensed Chemical DictionarySixth Edition, Reinhold Co., pp. 591 and 1042 relied on.

JOHN H. MACK, Primary Examiner.

W. VAN SISE, Assistant Examiner. 

1. IN A PROCESS OF ELECTROLYTIC FACSIMILE RECORDING WHEREIN AN ANODIC METAL IS DISSOLVED IN AN ELECTROLYTICALLY CONDUCTING RECORDING MEDIUM BY ELECTROCHEMICAL OXIDATION OF THE METAL TO FORM SOLUBLE METAL IONS AND THE DISSOLVED METAL IS DEPOSITED ON THE RECORDING MEDIUM AS A MARKING SUBSTANCE, THE IMPROVEMENT WHICH COMPRISES EMPLOYING AS THE RECORDING MEDIUM A SUPPORT IMPREGNATED WITH AN ELECTROLYTICALLY CONDUCTING SOLUTION CONTAINING A FORMALDEHYDE SULFOXYLATE REDUCING AGENT IN AN AMOUNT SUFFICIENT TO DEPOSIT SAID DISSOLVED METAL ON THE MEDIUM AS A MARKING SUBSTANCE. 